Cassette system for peritoneal dialysis machine

ABSTRACT

A peritoneal dialysis (PD) system that includes a disposable PD cassette including a base having a substantially planar portion and a dome-shaped protrusion extending from the substantially planar portion and a flexible membrane attached to the base and covering a recessed region of the dome-shaped protrusion to form a pumping chamber between the flexible membrane and the recessed region of the dome-shaped protrusion. The system also includes a PD machine including a deck and a door hinged from one side to the deck. The door and the deck can cooperate to form a cassette compartment, and the door has a cylindrical recess positioned to receive the dome-shaped protrusion of the base of the disposable PD cassette when the disposable PD cassette is disposed in the cassette compartment and the door is closed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of and claims priority toU.S. application Ser. No. 11/515,359, filed on Aug. 31, 2006, entitled“Improved Cassette System for Peritoneal Dialysis Machine,” which is acontinuation-in-part application of and claims priority to U.S.application Ser. No. 11/069,195, filed on Feb. 28, 2005, entitled“Portable Apparatus for Peritoneal Dialysis Therapy,” each of which isincorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates generally to apparatus for the treatmentof end stage renal disease. More specifically, the present inventionrelates to portable apparatus for the performance of peritonealdialysis.

Dialysis to support a patient whose renal function has decreased to thepoint where the kidneys no longer sufficiently function is well known.Two principal dialysis methods are utilized: hemodialysis; andperitoneal dialysis.

In hemodialysis, the patient's blood is passed through an artificialkidney dialysis machine. A membrane in the machine acts as an artificialkidney for cleansing the blood. Because the treatment is extracorporeal,it requires special machinery and a visit to a center, such as in ahospital, that performs the treatment.

To overcome this disadvantage associated with hemodialysis, peritonealdialysis (hereafter “PD”) was developed. PD utilizes the patient's ownperitoneum (a membranous lining of the abdominal body cavity) as asemi-permeable membrane. With its good perfusion, the peritoneum iscapable of acting as a natural semi-permeable membrane.

PD periodically infuses sterile aqueous solution into the peritonealcavity. This aqueous solution is called PD solution, or dialysate forshort. Diffusion and osmosis exchanges take place between the solutionand the blood stream across the peritoneum. These exchanges remove thewaste products that the kidneys normally excrete. The waste productstypically consist of solutes like urea and creatinine. The kidneys alsofunction to maintain the proper levels of other substances, such assodium and water, which also need to be regulated by dialysis. Thediffusion of water and solutes across the peritoneal membrane duringdialysis is called ultrafiltration.

In continuous ambulatory PD, a dialysis solution is introduced into theperitoneal cavity utilizing a catheter, normally placed into position bya visit to a doctor. An exchange of solutes between the dialysate andthe blood is achieved by diffusion.

In many prior art PD machines, removal of fluids is achieved byproviding a suitable osmotic gradient from the blood to the dialysate topermit water outflow from the blood. This allows a proper acid-base,electrolyte and fluid balance to be achieved in the body. The dialysissolution is simply drained from the body cavity through the catheter.The rate of fluid removal is dictated by height differential betweenpatient and machine.

A preferred PD machine is one that is automated. These machines arecalled cyclers, designed to automatically infuse, dwell, and drain PDsolution to and from the patient's peritoneal cavity. A cycler isparticularly attractive to a PD patient because it can be used at nightwhile the patient is asleep. This frees the patient from the day-to-daydemands of continuous ambulatory PD during his/her waking and workinghours.

The treatment typically lasts for several hours. It often begins with aninitial drain cycle to empty the peritoneal cavity of spent dialysate.The sequence then proceeds through a succession of fill, dwell, anddrain phases that follow one after the other. Each phase is called acycle.

Unlike hemodialysis machines, which are operated by doctors or trainedtechnicians, PD cyclers may be operated by the patient. Furthermore,many PD patients travel, which means taking their PD cyclers with them.Thus the insertion and operation of the cassette interface should be asergonomic, safe and foolproof as possible, while exhibiting enhancedperformance. The all-important design of the cassette itself shouldpermit the maximum flexibility in functionality.

The intent of this invention is to provide improved PD equipment with afocus on the design of the cassette and cassette compartment of the PDcycler.

SUMMARY OF THE INVENTION

In one aspect the invention includes apparatus peritoneal dialysisapparatus including a disposable cassette compartment defined by a decklying in a plane inclined from the vertical by about 10 to about 35degrees, preferably about 20 to about 25 degrees, and more preferablyabout 22 degrees, having openings for valve actuators and piston headsand a door hinged from the side so as to close in parallel over the deckand enclose the cassette within the compartment. In one embodiment, thecassette has inlet/outlet connections along the bottom of the cassette,the compartment accommodating the connection of vertically hanging tubesto the inlet/outlet connections on the cassette so that preferably allof the inlet/outlet connections are in a line along the bottom edge ofthe cassette. In this configuration the lines are permitted to make agentle bend substantially greater than 90 degrees when sitting on a flatsurface.

In another aspect of the invention, a disposable PD solution routingcassette compartment is defined by a door and a cassette deck, and aninflatable pad carried by the door forces a cassette that fits into thecompartment into sealing engagement with the cassette deck when the dooris closed and the pad is inflated. In addition a door latch mechanismcan be locked merely by the force of the inflatable pad tending to pushthe door away from the cassette deck.

In another aspect of the invention a disposable PD solution cassettedefining channels, valves and pump chambers for routing PD solution toand from inlet/outlet connections on the cassette is arranged in acassette compartment with a cassette deck for sealingly engaging thecassette, the cassette having a diaphragm covering at least one pumpchamber facing the deck, the deck having a reciprocating piston headmounted for reciprocation in a cylindrical chamber, an annular spacesurrounding the piston head between the chamber walls, and a pneumaticsystem draws a vacuum in the cylindrical chamber, the vacuum drawing thediaphragm tight against the piston head so that the diaphragm retractswith the piston head. The pneumatic system can also be used to seal apressure reading area of the cassette to a pressure sensor on the deck.

A further aspect of the invention is the design of a disposable cassettefor routing PD solution with a molded plastic panel having acircumferential fluid channel defined along the perimeter of the panel.

Finally, another aspect of the invention involves a method of operatinga PD machine, for example, using a cassette system with some of thefeatures disclosed herein, to drain spent PD solution from the patientto an empty solution bag that had been filled with PD solution earlierthat was used to infuse the same patient to take a sample of the used PDsolution.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a PD cycler.

FIG. 2 is a perspective view of the PD cycler of FIG. 1 on a specialcart with a heater bag on the heater tray and additional PD solutionbags for more exchanges hanging off the cart.

FIG. 3 is an end view of the PD cycler of FIGS. 1 and 2 showing theangle of the front and the heater bag outlet.

FIG. 4 is a perspective view of the cassette holder of the PD cycler ofFIG. 1.

FIGS. 5 and 6 are end views of the bracket and cassette deck of anembodiment of the cassette holder of FIG. 4 showing the angle of thecassette deck.

FIGS. 7A and 7B are exploded perspective views of the cassette holder ofFIG. 4, FIG. 7A showing the front of the cassette deck and doorassembly, and Fig. B showing the back of the cassette deck and internalcomponents behind the cassette deck, as well as the safety clamp

FIG. 8 is a perspective view of the front of the cassette deck of FIGS.5 and 6.

FIG. 9 is a detail perspective view of the front of the cassette deck ofFIG. 8 with one of the mushroom piston heads removed.

FIGS. 10A and 10B are perspective views of the cassette holder of the PDcycler of FIG. 2 showing the displacement of the door cassette pad whenpressurized from the retracted uninflated position in FIG. 10A to thefully inflated, extended position in 10B, which of course only happenswhen the door is closed with the cassette in place.

FIG. 11 is a view of a cassette used in the apparatus of the invention,the view being of the side that faces the cassette deck, i.e., themachine, when inserted.

FIG. 11A is a perspective view like those of FIGS. 10A and 10B, butshowing a cassette installed in the cassette compartment before closingthe door.

FIG. 12 is a hydraulic schematic for the liquid lines of the cassetteand tubing for the cycler of FIG. 2, indicating the valves by number onthe cassette of FIG. 11.

FIGS. 13A, 13B and 13C illustrate various PD solution flow paths throughthe cassette of FIG. 11.

FIG. 14 is a pneumatic schematic for the pressure and vacuum sides ofthe system for actuating the cassette valves and other pneumaticcomponents of the cycler of FIGS. 1 and 2.

FIG. 15 is a schematic and block diagram of the electronic operation ofthe PD cycler of FIGS. 1 and 2.

FIGS. 16 and 17 illustrate aspects of the user interface.

Numbers referring to the same items in several drawings will bear thesame reference numbers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The Door SealingMechanism

Referring to FIG. 1, the portable PD apparatus of the invention is shownin an embodiment of a PD cycler 10. The housing 20 holds a touch screen22, along with additional control buttons 22A forming the control panelfor the user interface operated by the patient. A cassette holderincludes a hinged door 24 and a cassette support deck 26. The cassette28, shown in FIG. 4, fits into the cassette support deck 26. A cassetteis inserted into the support deck 26 and the door 24 is closed on thecassette and securely latched, as will be described later.

FIG. 2 shows the PD cycler 10 with some of its accessories to illustratehow it used. The cycler 10 is seated on top of a cart 12 designed toaccommodate the PD solution bags and associated tubing. The disposablecassette 28 (FIG. 1) locked inside door 24 includes channels, flexiblevalve domes and diaphragm covered pumping chambers described below thatare actuated by mating pneumatic valves and pistons interfacing with thecassette compartment to route the flow of PD solution from the bagsthrough the cycler to the patient and from the patient to a drain. Thecassette itself has tubing connectors 16 arrayed along its bottom edge.The connectors extend beneath the door 24 and are connected to tubing asshown in FIG. 2.

PD solution bags 18 are suspended from fingers on the sides of the cart12 as shown. A heater bag 19 is shown lying in a shallow concavedepression forming the heater tray 21, which is sized and shaped toaccommodate a typical 5 L bag of PD solution. The heater tray 21 has aplurality of heating coils (not shown) embedded below the surface. Thesurface of the tray 21, as better shown in FIGS. 1 and 3, is slightlyinclined downward to the right to assist in emptying the heater bagwhich is arranged so that the outlet 19A of the heater bag is also atthe right side, adjacent to a temperature sensor 23 positioned in thesurface of the heater tray 21 to track the temperature of the solutionin the heater bag for a thermostatic control circuit that turns theheating coils on and off as needed to maintain the PD solution at thedesired temperature. A dual voltage heating system for the heater tray21 is disclosed in accompanying application Ser. No. 11/513,618, filedthe same day as this application, by Kulwinder Plahey, assigned to thesame assignee, entitled “Peritoneal Dialysis Machine with Dual VoltageHeater Circuit and Method of Operation,” which is incorporated byreference herein in its entirety. The dual voltage heating systemautomatically reconfigures the heating circuit depending on detection ofeither 110 VAC or 220 VAC to deliver the same wattage for heating PDsolution before delivery to the patient, thus facilitating use of thesame machine in the United States and Europe.

The heater tray 21 is also mounted internally on a support equipped witha load cell (not shown) to provide an electrical signal indicating theweight of the contents of the PD solution bag to tell the cycler controlsystem how full the heater bag is with PD solution. Referring to FIGS.4, 5, 6, 7A, 7B, 8, 9, 10A and 10B, the cassette compartment 60 will nowbe described in detail. Essentially, the cassette compartment 60consists of a base 30 and door 24 hinged to the base 30 on the rightside, as shown in FIG. 4. Base 30 incorporates two pumps 44 havingexposed mushroom heads 32. Mating with these heads are two cylindricalchambers 34 that accommodate the rigid domes for the pump chambers onthe cassette 28 within door 24. The base 30 also includes a pair of doorlatches 36 that mate with holes 38 in door 24. The door also has asliding latch 40 or catch slide. Microswitch 42 provides an electricalindication of whether the door is opened or fully closed.

It is necessary that a very tight, secure mechanical enclosure beprovided with intimate contact with the cassette 28 (FIG. 4) when themachine is in operation. Prior art PD machines provided this tightenclosure by using a tight door latch that had to be almost forcedclosed by the patient. This created a problem for elderly or very illpatients who lacked the strength to close the door. Alternatively, inother prior art PD machines, cassettes were inserted using a complicatedmechanism, similar to a VCR, making servicing more difficult.Accordingly, the PD apparatus of this invention does not require thepatient to close the door with sufficient force to make all thenecessary seals. Furthermore, the cassette can be set directly intocompartment 60 without use of the more complicated, VCR-like apparatus.

Door 24 is lightly latched using latch lever 40 and latch posts 36,which loosely engage with holes 38. Although the door easily “clicks”shut, the proper seals are not made by this closing. To insure that thecassette 28 is in intimate and sealed contact with both the base 30 andthe door 24, the PD apparatus of the invention uses an inflatable pad47, shown in FIG. 7A. In front of the pad 47 is a displaceable spacer 49mounted to the pad 47 by means of a plate 58. One or more molded plasticpressure pads 51 are bonded to the front of the spacer 49 for engagingthe cassette. The cassette is held in place between the cassette pad 51and the cassette deck 26, as shown in FIGS. 4 and 7A. Once the door islightly shut and latched by the patient, and the system receives asignal to that effect from microswitch 42, pressurized air is pumpedinto pad 47, squeezing the cassette between the door 24 and the cassettedeck 26, as shown in FIG. 4. The pressure applied should be adequate sothat all necessary seals are made. Thus even though the cassette willwind up being under pressure, the patient does not need to exert anyforce on the door or latch to close the door.

To open door 24 to load a cassette, button 50 on the top left edge ofthe door (FIG. 4) is depressed. This will disengage the door lock. Thedoor then swings open from left to right. Cassette 28 (FIG. 11) may thenbe loaded into cassette holder by putting the top of the cassette underthe locating pins 52. The bottom edge of the cassette will be snapped inplace over a spring loaded center clip 53 (FIG. 4). The door 24 closesfrom right to left pushing gently on it to automatically engage the doorwith latch posts 36. The catch assembly is comprised of a catch slide 40a mounting slide block 41 to which it is attached (FIG. 7A) and a catchtension spring (not shown). The block slides in a machined slot 54 onthe left side of the door as viewed in a closed position (FIG. 4). Asthe door swings shut, the catch slide comes in contact with the beveledend 56 of the latch posts 36. The action of lightly pushing on the doorto latch it also actuates the door safety switch 42. The catch slidelowers and then springs upward in the notches formed by the latch posts36, coming to rest with the flat blade of the catch slide in contactwith the forward planar wall of the notches in the latch posts. When thedoor is not pressurized the friction between the contact area of thelatch post notch walls and the catch slide blade is easily overcome tore-open the door. However, when the compartment is pressurized by theinflatable pad 47, the friction between these elements cannot beovercome by the user who will be unable to push the catch slide 40downward with enough force to overcome the contact friction with thepost notch walls. Thus the pressurization of the door acts as a safetyinterlock for the cassette compartment.

Once the door safety switch is closed, the system receives an electricalsignal indicating that it is ready to clamp the cassette into thecassette holder by inflating the cassette clamping inflatable pad 47((FIG. 3A) with approximately 37 psi pressure (which generatesapproximately 1000 pounds of force). This clamps the cassette 28 againstthe clamp pad 51 (FIG. 3A), thereby rigidly holding the cassette inplace so that it can be operated by the valves and pistons in thecassette deck. The door locking mechanism is then immobilized,preventing the door from accidentally opening or even from being openedby the patient, for safety purposes.

There are several ergonomic features of the basic arrangement of thecassette compartment 60 and door 24. As shown in the end views in FIGS.5 and 6, the brackets 57 that hold the base 30 of the cassette deck andalso support the hinges 59 for the door, are designed to hold the baseand door at a 10 to 35 degree angle to the vertical, preferably 22degrees. Thus the hinge line of the door itself is inclined rather thanplumb and the deck 36 where the cassette is mounted is also in areclining orientation. When the user opens the door as shown in FIGS. 1and 10A, for example, the door tends to hold itself open when openedpast 90 degrees because of this inclination. In addition, the surface ofthe deck where the cassette is to be mounted is more easily viewed andaccessed by the user because of the angle, particularly because thecompartment would rarely be at eye level. The user must assure that thecassette is inserted correctly with the notches 28A (FIG. 11) under thepins 52 (FIG. 4) and the lower center edge of the cassette 28B snappedin place over the clip 53. (Note that the side of the cassette 28 inview in FIG. 11 is the one that fits against the cassette deck, so whenin place, the cassette 28 will appear reversed.) This is more easilyaccomplished with the compartment at this approximate angle.

A further advantage of the cassette compartment design is achieved byvirtue of the door being hinged from the side. With this arrangement,the cassette is free to have the tubing connections (inlets andoutlets), of which there are typically seven in use, arrayed along thebottom edge of the cassette as shown in FIGS. 1 and 11 with the tubinghanging straight down. This permits the tubes to hang free anduntangled, straight down under the force of gravity if there is a sloton the table as shown in FIG. 2 without any unnecessary bending likelyto kink or constrict the lines. In combination with this bottom entryfeature, the 22 degree angle of the door compartment better accommodatesa bend in the lines if the cycler is sitting on a night table forexample where the lines would extend downward and then across the tabletop for a few inches. If the compartment was vertical the lines wouldhave to make a 90 degree turn. Instead they can take a gentler 112degree turn on the table top or other flat surface and remain free ofconstriction.

The Pump

The pumps 44 (best seen in FIG. 7B) are controlled by stepper motors 45.The details of the stepper motor control will be explained later. The PDapparatus of the invention uses two modes of pumping, simultaneous andalternating. With the alternating method, while one pump is protracted,the other is retracted. Simultaneous pumping is where both pump headsextend at the same time in the same direction, and both retract at thesame time. Each pump has a piston with a mushroom shaped head 32 asshown in FIGS. 4 and 5. The mushroom head 32 has a threaded bore whichscrews onto a threaded post 65 on the piston shaft as shown in FIG. 5.The outer diameter of the head 32 is slightly less than the innerdiameter of the cylinder 55 in which the head reciprocates as shown inFIG. 9. The inner wall of each cylinder has a slot (not shown) in theform of a circumferential arc in the wall to allow evacuation of airfrom the piston chamber, as described below.

To move fluid out of one of the pump chambers, the mushroom head 32mated to that chamber is protracted all the way to the rigid back domeof the cassette 28, but not touching it. To draw fluid into one of thepump chambers, the piston head 32 is pulled back by one of the steppermotors 45. The vacuum in the piston chamber causes the diaphragmmembrane covering the pump chamber on the cassette to be sucked flushagainst the spherical surface of the piston head. The diaphragm isexposed to the vacuum approximately −500 millimeters of mercury in thepiston chamber by way of the annular space surrounding the circumferenceof the piston head where it comes closest to the cylindrical wall of thepiston cylinder 55. The periphery of the diaphragm remains sealedairtight against the cassette deck 26 because of the pressurized doordue to its inflatable pad. Thus the vacuum in the piston chamber isbounded by the cylindrical wall, the cassette diaphragm and the pistonitself. Thus when the piston head retracts, the vacuum continues to holdthe diaphragm against the mushroom head and the diaphragm retracts withthe piston to thus enlarge the chamber, drawing fluid into one of thechambers A or B of the cassette 34 through whichever valve is opened.

For draining fluids from the patient, an alternating pumping method isemployed where one pump 44 extends while the other retracts. When thepump associated with chamber A is extending, the fluid in the chamber Ais pushed out into a drain line of the cassette 28. As the pumpassociated with chamber B retracts, fluid from the patient is drawn intochamber B. When this motion is completed, the pump associated withchamber A then retracts and draws fluid from patient while pump Bprotracts and transfers fluids out into the drain line. This processcontinues until the required volume of fluid from the patient isprocessed.

Initially, the pumps 44 are moved to a home position which is sensed bya conventional optical sensor, not shown. The pump controller encodervalue is then set to zero. Next the pump is moved towards the cassetteuntil it touches the cassette. This is the “OUT” position where theencoder is then set to a current encoder value less a maximum(calculated to be the maximum possible stroke, for example, an encodercount of 250). Then, the pump is moved backwards by 800 microsteps, orabout an encoder count of 16000. The “HOME” position is then set to thisencoder value. The stepper motor 45 next moves backward another 500microsteps, or about an encoder count of 10,000. This is where the “IN”position is set.

Volume calculation is based on the fact that the cassette volume is aknown value (based on its physical dimensions). The volume of the pumphead is also a known value (again, the calculation of this volume isbased on the physical dimensions of the pump head and chamber). If thewhole mushroom head 32 is flushed against the cassette wall 46, then nofluid volume can reside in the cassette chamber. As the mushroom head 32is moved back, however, it draws fluid into the chamber of the cassette28 (FIG. 4). The volume of fluid drawn into the chamber is calculated bysubtracting the volume of the mushroom head 32 that remains in thechamber from the volume of the chamber. To calculate how much volume ofthe pump head resides inside the chamber, the amount of linear travel ofthe pump is calculated, and this distance correlates to the distance oftravel of the mushroom head. From that distance a formula is used todetermine how much fluid volume still resides in the chamber.

The Electronic Controls for the Pump

The electronics board 101 of the PD apparatus of the invention is shownin FIG. 6. Stepper motor 100, which drives each pump of the PD apparatusof the invention, is controlled conventionally using firmware withsignals to stepper motor driver 108. The firmware resides in two flashmemories 102 and 104. The firmware stored in flash memory 102 is used toprogram the bridge field-programmable gate array (FPGA) 106. Thefirmware stored in the flash memory 104 is used to program the MPC823PowerPC microprocessor 112.

Referring to FIG. 2, a stepper motor 45 drives a conventional lead screw(not shown) which moves a nut (also not shown) in and out on the leadscrew. The nut, in turn, is connected to a mushroom head 32 whichactually makes contact with the membrane A or B on the cassette 28 (FIG.4). The stepper motor and lead screw are chosen to provide the requiredforce to push fluid out of the cassette following the opening of fluidpaths in cassette, as will be described later. The stepper motor 45preferably requires 200 steps to make a full rotation, and thiscorresponds to 0.048″ of linear travel. Additionally, an encodermeasures the angular movement of the lead screw. This measurement can beused to very accurately position the mushroom head assembly.

A stepper motor controller (not shown) provides the necessary current tobe driven through the windings of the stepper motor. The polarity of thecurrent determines whether the head is moving forward or backward. Roughpositioning of the piston is aided by one or more opto-sensors (notshown).

Inside the FPGA 106, there are two duplicate sets of control logic, onefor each piston. The two-channel quadrature output of the linear encoder110 (FIG. 6) is converted into an increasing or decreasing count. Theoverall range of this count is from 0 to ˜65,000 (or, the count can besplit in half about 0, from −32,499 to +32,500). This count is requiredto determine the current position and subsequent movement of the piston.There is a direct correlation between actual movement of the lead screwand an encoder value.

Referring again to FIG. 6, the FPGA 106 makes a comparison between thecurrent encoder input and a target value. This is needed for automaticmovement. A single command to the FPGA 106 initiates a complete cyclethat ends with the piston being moved from its current position to newlydesignated position. Additionally, the FPGA 106 can automatically stopthe motor movement. This is desirable, for example, where the pump headreaches its end of travel (sensed by end of travel switch 112, or wherethe pumping action causes the pressure to be out-of-bounds. If thepiston reaches an end-of-travel switch 112, the automatic movement ishalted. Likewise, if a pressure sensor 48 (FIG. 2) determines that thepressure is outside of the prescribed, limited range, the motors 45(FIG. 2) can be halted to prevent a larger excursion, which might beharmful to the patient.

Another part of the FPGA firmware allows the speed of the stepper motors45 to be controlled, as is well known in the art. By adjusting the motorpulse duration and time between pulses, the motor can run faster orslower to get a desired speed vs. torque balance. The speed the motorruns is inversely related to the torque it is able to apply to the pumphead. This adjustment allows the machine to produce the desired amountof push on the fluid in the pump chambers A or B (FIG. 4) so that itflows easily through the lines, but isn't forced so as to triggerpressure alarms or cause rupture of the lines. On the other hand, if youtry to run the motor too fast, you may lose the necessary torquerequired on the pump head to move the fluid through the line.

In addition to the motor pulse, the FPGA 106 provides several controlsignals to the stepper motor controllers (not shown), for example,direction and step size. Depending on the values sent from the flashmemories 102 and 104 to the FPGA 106, the step size can be adjustedbetween full, half, quarter and eighth steps. Also, the motor controllercan be sent a continuous sequence of pulses for rapid motor movement, orjust a single pulse to make a single step. This is set conventionally byregisters in the FPGA 106.

The Cassette

The cassette itself is shown in more detail in FIG. 11. The cassette isa biocompatible plastic molded part which has a rigid plastic backfacing away from the viewer in FIG. 11. The side that faces the cassettedeck as shown in FIG. 11 includes channels and small dome shapedflexible pod like diaphragms forming occludable valves numbered 1through 16. The intermediate size dome shaped diaphragms cover thepressure sensor chambers P on the cassette facing the deck 26, andfinally two large flexible diaphragms cover the clamshell (whenexpanded) shaped pumping chambers A and B. The diaphragms are facing theviewer in FIG. 11 but would be flush against the piston heads and othermating components of the cassette deck when installed in the cycler. Theinlet/outlet valves across the bottom of the cassette are from right toleft as follows:

6 Patient line 7 N/A (pediatric option) 11 Solution bag No. 1 12Solution bag No. 2 13 Solution bag No. 3 14 Last solution bag 15 Heaterbag 10 Drain A Pump chamber B Pump chamber P Sensors

The cassette 28 is shown installed in FIG. 11A with its rigid plasticback now facing the viewer and the lines reversed. The inlets andoutlets as shown in FIG. 11A are formed with capsule like connectors 28Cthat allow connection to the tubing set. The connectors 28C project outof the plane of the cassette 28 and fit into mating recesses 51C on thedoor plate 51, as shown in FIG. 11A. Also shown in FIG. 11A is thesafety clamp 71 also shown in FIGS. 4 and 7B. The clamp acts to closeall of the inlet/outlet connections in an error situation as describedin the description of the pneumatic system below.

The valves in the cassette control and route the flow of PD solutionthroughout the PD system under the control of a hydraulic network shownin FIG. 12. The valves are designated V1-V16 and correspond to thenumbered valves in FIG. 11. The flow lines in the schematic areimplemented by the cassette's preformed channels. The valves areactuated pneumatically to case various sources and destinations to beplaced in fluid communication. For example, for fluid to flow from Bag 1(one of the bags 18 hanging on the cart 12 in FIG. 2), valve V11 isopened and pump valve V1 is opened while the piston head for chamber Ais retracting to fill the chamber, then V1 is closed and V2, V16, V9 andV15 are opened while the piston head 32 protracts into the chamber Adriving liquid out into the heater bag. Other examples are shown inFIGS. 13A, 13B and 13C.

One other design feature of the cassette 28 which is not found in othercassettes is the circumferential channel 28D formed in the cassette.Channel 28D actually circumnavigates the entire periphery of thecassette passing valves 16, 9, 5 and 8. This channel also passes by allof the inlet/outlet ports on the bottom of the cassette. Thus theinterconnected circumferential channel 28D has multiple uses indelivering fluid to and from the pump chambers A and B. This arrangementalso potentially affords an opportunity for flushing the all of thelines of the cassette by appropriate valve openings. For example, fluidcould be introduced under pressure from the drain outlet 10 and forcedall the way around the cassette and out the rest of the ports 6, 7 and11-15.

Description of Fluid Flow Through the Machine

The fluid flow through the disposable cassette 28 is illustrated inFIGS. 13A-13C. The PD machines of the invention utilize sixfluid-processing sequences: flush, prime, drain, fill, pause and dwell.The purpose of the flush sequence is to remove air from all the lines(except the patient line) and from the cassette. This is accomplished bypumping dialysate solution through the lines to be flushed.

The prime sequence removes air from the patient line by pumpingdialysate solution through the patient line. The drain sequence is usedto pump dialysate solution from the patient to the drain. The fillsequence is used to pump dialysate solution from the heater bag to thepatient. The pause sequence allows the patient to disconnect from the PDmachine once the patient has been filled with dialysate solution. Whilethe patient is disconnected from the machine, the machine will betransferring dialysate solution from the solution bags to the heaterbag. Finally, the dwell sequence is used to allow the dialysate solutionto remain for a set time in the patient. Dwell sequences are identicalto pause sequences with the exception that the patient does notdisconnect from the machine. While a dwell sequence is occurring, themachine will be transferring dialysate solution from the solution bagsto the heater bag.

Each figure contains a dashed or solid line, each line having arrowsthat indicate the direction of flow. All flow diagram lines that are thesame pattern (i.e., either dashed or solid) occur at the same timeduring the process. The different line patterns thus represent alternatetimes.

For example in FIG. 13A, in the “Heater to Patient” line diagram, whenpump chamber A is filling, chamber B is emptying. The dashed linesindicate that pump A is retracting to pull dialysate solution from theheater bag. At the same time pump B is protracting to pump dialysatesolution through the patient line. The solid lines indicate that pump Ais protracting to push dialysate solution to the patient. At the sametime, pump B is retracting and pulling dialysate solution from theheater bag.

FIGS. 13B and 13C show more of the flush sequence as the dialysatesolution comes from the supply and moves through the drain line.

FIG. 13A illustrates the prime sequence as the solution from the heaterbag pushes air out of the patient line, as well as the fill sequencewhere solution from the heater bag is pumped to the patient. FIG. 13Cillustrates the drain sequence as the solution is pulled from thepatient and pumped to the drain.

Solution may be pumped from a solution bag to the heater bag while thepatient is disconnected (pause mode) or still connected (dwell mode), asshown in FIGS. 13B and 13C.

Owing to the flexibility of the flow paths that can be created bymanipulating the balloon valves in coordination with the pumps, anynumber of other flow paths can be utilized. One possibility would be todrain fluid from the patient during a portion of the drain operation tolines other than the drain line. For example, The patient line could beconnected for a period of time during the drain mode to divert some ofthe spent PD solution from the patient line into one of the emptysolution bags to collect a sample for testing.

The Pneumatic System

Referring to FIGS. 4 and 14, a pneumatic system provides pressure tooperate the valves and fill the inflatable pad 47 to seal the doorclosed and vacuum to seal the flexible cassette diaphragms to the matingmembers on the cassette deck 26, namely the mushroom heads and pressuresensors. The basic schematic for the components of the pneumatic systemare shown in FIG. 14. A compressor pump is used to provide either air ora vacuum in corresponding reservoirs. On the right side of FIG. 14 asshown, is the pressure tank which is drawn on as necessary to pressurizeand maintain the pressure in the inflatable pad 47. During the pumpingsequence, this air and vacuum resource is used to inflate and deflatethe balloon valves 48. When inflated, a balloon valve will block thefluid from moving through the particular one of channels 1-16 (FIG. 4)of the cassette that mates with the selected one of balloon valves 48.When a balloon valve is deflated, the fluid can move freely through thatparticular channel controlled by that balloon valve.

Another function of the pneumatic system is to pressurize the safetyclamp 71 shown in FIGS. 4, 11A and 7B. As shown in FIG. 7B, the barshaped clamp below the cassette deck is spring loaded and acts like a“dead-man” brake switch. Pneumatic pistons operated by the pneumaticsystem retract the clamp against the spring force when pressurized thuswithdrawing the clamp 71 away from the door 24. As shown in FIG. 11A,the clamp extends across all of the tubing connected to the cassette andin the absence of pressure will crimp closed all seven of the tubesshown in FIG. 11A against the bottom of plate 51 in the door 24. Thishappens automatically when the machine's controller senses some out ofbounds condition that makes it unsafe to continue the operation, such asover-temperature of the heater bag, or rupture of one of the lines orexcessive patient pressure, or loss of power.

The Pressure Sensors

Referring to FIGS. 4 and 11, a very important requirement of the PDapparatus of this invention is the accurate measurement and control ofpressure between the fluid reservoirs and the patient. If the pressureon a line to the patient increases above alarm limits, serious harm canbe caused to the patient. The PD system itself needs to operate atpressures that far exceed the limit. These high pressures are needed forto operate the pressure sensors, balloon valves and other functions inthe cassette. Therefore these pressures need to be kept independent fromthe pressures seen by the patient. Appropriate and reliable sealing andvalving needs to be used to keep these high pressures away from thepatient.

Referring to FIG. 4, to monitor the pressure in the system, two pressuresensors 33 are utilized to indirectly detect the pressure and vacuumwithin the patient's peritoneum. These sensors are preferably solidstate silicon diaphragm infusion pump force/pressure transducers, forexample Model 1865 made by Sensym Foxboro ICT. When cassette 28 (FIG. 4)is inserted into the cassette compartment 60, the pressure sensing areas“P” within the cassette 28 (FIG. 11) line up and are in intimate contactwith the two pressure sensors 33. These sensing areas P are connected,respectively, directly to each chamber A and B through canals 62 and 64,respectively, so that when fluid moves in and out of the chambers A andB, the pressure sensors 33 can detect its presence. The cassettemembrane comprising two areas marked “P” adheres to the pressure sensors33 using vacuum pressure in the same manner as the diaphragms of thepump chambers A and B are sealed against the mushroom head. Clearancearound the pressure sensors communicates vacuum to the pressure domediaphragms the circumferences of which are sealed airtight to thecassette deck by the pressurization of the door compartment.

The two pressure sensors 33 are connected to a high resolution 24 bitSigma-Delta, serial output A-D converter (ADC) 103 on I/O board 101.This ADC sends a signal from each of the two pressure sensors to theFPGA 106 on the board 101. After the data ready signal is received bythe FPGA 106, the FPGA reads this ADC and transfers this data to beprocessed by the microprocessor 112, which in the preferred embodimentof the invention is an MPC823 PowerPC device manufactured by Motorola,Inc.

On completion of the flush and prime processes, as is well known in theart, the cassette will be filled with solution. At this time, the lineto the patient will be completely filled with solution. The pressure atthis stage is detected and will be used as base line for staticpressure. At that time, the patient's head height relative to the PDmachine will be determined from the differential in the pressurereading. Preferably, this pressure differential is maintained below 100mbar.

During the drain sequence, the maximum pump hydraulic vacuum is limitedto −100 mbar to prevent injury to the patient. The vacuum in theperitoneum must be held at or above this value. The position of thepatient below or above the PD machine level indicated by the staticpressure measurement is compensated by adjusting the level of thevacuum.

By way of example, the target vacuum of the vacuum chamber can be basedon the following equation:

Pstat=static hydraulic pressure(+1 meter=+100 mbar and −1 meter=−100mbar)

Ppatmax=−100 mbar

Pvac=target vacuum of vacuum chamber

Pvac=Ppatmax+Pstat

For example, where the patient is 1 meter above the PD machine, thedifferential pressure=+100 mbar; Pvac=−100 mbar+100 mbar=0 mbar.

Where the patient on same level than machine, the differentialpressure=0 mbar;

Pvac=−100 mbar+0 mbar=−100 mbar.

Where the patient is 1 meter below machine, the differentialpressure=−100 mbar;

Pvac=−100 mbar+−100 mbar=−200 mbar.

Since continuous flow through the various lines connected to the patientis essential to proper treatment of the patient, it is important tocontinuously monitor if a patient line is blocked, partially blocked oropen. There are three different possible situations:

-   -   1. the patient line is open;    -   2. the patient line is closed; or    -   3. the patient line is not completely open and therefore creates        an undesired flow resistance (caused, for example by the patient        is lying on the line).

The pressure sensors 33 (FIG. 2) can be used to detect error conditions.Referring to FIG. 5A, when the pump B is protracting and thereby pumpingdialysate fluid into a line that is open to patient, it is veryimportant that the patient pressure and the encoder values are carefullymonitored, using the pressure sensors 33 described above. Three possibleerror situations may occur, for example, as a result of the followingevents:

-   -   1. The patient line is open when pump B is protracting until a        defined length value is reached, and the patient pressure is not        increasing;    -   2. The patient line is closed, and the pump is not able to        protract because the patient pressure increases to a defined        alarm limit.    -   3. The pump protracts to produce an increasing patient pressure,        but the pressure decreases slowly.

These error conditions may be sensed using the pressure sensors 33 ofthe invention, and corrective action can then be taken, eitherautomatically or by sending an alarm to the patient, where the screentells the patient what action to take. For example, the screen may tellthe patient that he or she may be lying on a fluid line, and should moveoff of it.

Since the patient pressure sensors are critical components to patientsafety, it is very important to monitor whether these sensors arefunctioning properly. Although prior machines have attempted toaccomplish this monitoring by checking the pressure readings from thesensors, such tests are not foolproof, because the varied nature of thenormal, expected readings may fool one to believe that the sensors areworking properly when actually they are not.

Therefore this sensor monitoring should be independent of the pressuremeasurements. In a preferred embodiment of the invention, the pressuresensors are monitored through an A-to-D converter (“ADC”) having twodedicated current sources, one for each sensor. On command, each ADCwill source current (instead of acquiring data, as is usual case) andmonitor how this current flows (or fails to flow) through each sensor.This independent monitoring of the pressure sensors would guaranteepatient safety. Since normal treatments typically run overnight, theability to continually double-check the very pressure sensors thatmonitor patient safety is indeed desirable.

The User Interface

One important part of a patient-controlled PD machine is the userinterface, shown in FIG. 7. A common problem with prior art machines isthat the patient loses track of the mode in which the machine isoperating. In the invention, the touch screen display has at least twoportions: one is a mode-indicating portion 80, and the other is anoperation descriptive portion 82.

The mode-indicating portion 80 has a plurality of touch sensitiveindicia 84, 86, 88, 90, and 92, each indicating the mode in which themachine is operating to keep the patient continually informed of whichone of at least three operating modes the machine is operating in. Thesemodes as illustrated in the preferred embodiment shown in FIG. 7. By wayof example and not of limitation, the modes may include: a treatmentmode 84, during which dialysis is taking place; a settings mode 86,where the treatment type settings of the PD machine are displayed andcan be modified by the patient; a diagnostic mode 88 where the operationof the machine is being diagnosed; a patient data mode 90, where patientdata is displayed; and treatment history mode 92, where prior treatmentof the patient is displayed.

During operation under any of these modes, the operation descriptiveportion 82 of the display changes to display details of the specificoperation being carried out within the selected mode. Generally, thedescriptive portion shows helpful information to guide the user inoperating the machine. For example, during treatment, when the treatmentmode indicator is highlighted, as shown in FIG. 7, the descriptiveportion 82 shows the patient that the next required step is to “Pushopen cassette door.” Alternatively, the descriptive portion may show thedirection of fluid flow, or provide an indication of the extent oftreatment completion or other description of the current stage oftreatment. The same kind of descriptions is provided for variousdiagnostic operations which take place in the diagnostic mode.

All five illustrated mode indicia in the mode portion 80 of the screen,for each of the five operating modes of the preferred embodiment, alwaysremain visible to the patient, with the mode that the machine iscurrently operating in being highlighted in some manner, as shown inFIG. 7 for the treatment mode indicator 84.

The operating mode is changed by the patient by touching one of theindicia on the screen different from the one (“treatment” in FIG. 7)that is currently highlighted. Unless there is some reason, such assafety or otherwise, that the mode must not be changed at that time, themode will change to the new mode when the patient touches the differenticon, and the newly selected icon 88, “diagnostics” as shown in FIG. 8,will be highlighted and the “treatment” icon 84 for the prior operatingmode will no longer be highlighted, as shown in FIG. 8.

Then the descriptive portion 96 of the touch screen, shown in FIG. 8,will display information pertaining to the new “diagnostics” mode ofoperation, such as a “treatment recovery warning” shown in FIG. 8. Icons84, 86, 90 and 92 for all the other four possible modes in the preferredembodiment will remain displayed, but not highlighted, so the patientalways knows (1) what mode the machine is operating in; and (2) whatother possible operating modes exist.

The invention has been described in terms of particular embodiments.Other embodiments are within the scope of the following claims. Forexample, steps of the invention can be performed in a different orderand still achieve desirable results.

1. A peritoneal dialysis (PD) system comprising: a disposable PDcassette comprising a base having a substantially planar portion and adome-shaped protrusion extending from the substantially planar portion,the dome-shaped protrusion defining a recessed region, a flexiblemembrane attached to the base and covering the recessed region of thedome-shaped protrusion to form a pumping chamber between the flexiblemembrane and the recessed region of the dome-shaped protrusion, and aplurality of tubing connectors positioned along one edge of the PDcassette; and a PD machine comprising a deck having a plurality ofopenings, a door hinged from one side to the deck, the door and the deckbeing arranged so that when the door is closed over the deck, the doorand the deck cooperate to form a cassette compartment configured toreceive the disposable PD cassette therein, and the door having acylindrical recess positioned to receive the dome-shaped protrusion ofthe base of the disposable PD cassette when the disposable PD cassetteis disposed in the cassette compartment of the PD machine with the doorclosed, a piston head at least partially disposed within one of theopenings of the deck, the piston head being aligned with the pumpingchamber of the disposable PD cassette when the disposable PD cassette isdisposed in the cassette compartment of the PD machine, and aninflatable bladder configured to compress the substantially planarportion of the base of the disposable PD cassette between the deck andthe door of the PD machine when the disposable PD cassette is disposedin the cassette compartment of the PD machine with the door closed andthe inflatable bladder is inflated.
 2. The PD system of claim 1, whereinwhen the PD machine is resting on a substantially horizontal surfaceduring use, the deck lies in a plane inclined from the vertical by 10 to35 degrees.
 3. The PD system of claim 2, wherein when the cassette isdisposed in the cassette compartment, all of the tubing connectors arein a line along a bottom edge of the cassette so that tubes connected tothe tubing connectors bend between the cassette and the substantiallyhorizontal surface on which the PD machine is resting, at an anglegreater than 90 degrees.
 4. The PD system of claim 3, wherein the tubingconnectors extend beneath the door of the PD machine.
 5. The PD systemof claim 1, wherein the cassette defines a circumferential channel thatextends along a perimeter region of the cassette, and thecircumferential channel can be placed in fluid communication with thepumping chamber.
 6. The PD system of claim 1, wherein the piston head isa mushroom-shaped piston head.
 7. The PD system of claim 6, wherein thepumping chamber is substantially clamshell shaped.
 8. The PD system ofclaim 1, wherein the PD machine further comprises a clamp that, when thecassette is disposed in the cassette compartment and tubes are connectedto the tubing connectors of the cassette, extends across all of thetubes such that all of the tubes can be crimped by the clamp at onetime.
 9. The PD system of claim 8, wherein the PD machine furthercomprises a controller that causes the clamp to crimp all of the tubeswhen a potentially unsafe condition is detected.
 10. The PD system ofclaim 1, wherein the pump chamber has an inlet port and an outlet port.11. The PD system of claim 1, wherein the PD machine comprises aplurality of inflatable balloon valves positioned in some of theopenings in the deck.
 12. The PD system of claim 1, wherein the PDmachine comprises two piston heads that travel back and forth throughtwo of the openings in the deck when reciprocated, the PD cassettedefines two pumping chambers, and the piston heads align with thepumping chambers when the PD cassette is disposed in the cassettecompartment of the PD machine.
 13. An apparatus for pumping fluidsbetween a peritoneal dialysis machine and a patient in order to performperitoneal dialysis on the patient, the apparatus comprising: adisposable cassette for routing PD solution, a cassette compartmentdefined by a deck and a door hinged from the side so as to close inparallel over the deck and enclose the cassette within the compartment,wherein the deck has openings for valve actuators and piston heads, andwhen the apparatus is resting on a substantially horizontal surfaceduring use, the deck lies in a plane inclined from the vertical by 10 to35 degrees.
 14. The apparatus of claim 13, wherein when the apparatus isresting on a substantially horizontal surface during use, the deck liesin a plane inclined from the vertical by about 20 to 25 degrees.
 15. Theapparatus of claim 14, wherein when the apparatus is resting on asubstantially horizontal surface during use, the deck lies in a planeinclined from the vertical by about 22 degrees.
 16. The apparatus ofclaim 13, wherein the cassette has inlet/outlet connections along thebottom of the cassette when the cassette is disposed in the cassettecompartment, the cassette compartment accommodating the connection oftubes to the inlet/outlet connections on the cassette.
 17. The apparatusof claim 16, wherein all of the inlet/outlet connections are in a linealong the bottom edge of the cassette so that when the cassette isdisposed in the cassette compartment and the tubes are connected to theinlet/outlet connections of the cassette, the tubes bend, between thecassette and a substantially horizontal surface on which the system isresting, at an angle substantially greater than 90 degrees.
 18. Theapparatus of claim 17, further comprising a clamp that, when thecassette is disposed in the cassette compartment and tubes are connectedto the inlet/outlet connections of the cassette, extends across all ofthe tubes such that all of the tubes can be crimped by the clamp at onetime.
 19. The apparatus of claim 18, further comprising a controllerthat causes the clamp to crimp all of the tubes when a potentiallyunsafe condition is detected.
 20. The apparatus of claim 13, wherein theapparatus comprises two piston heads that travel back and forth throughtwo of the openings in the deck when reciprocated.
 21. The apparatus ofclaim 13, wherein the apparatus comprises a plurality of inflatableballoon valves positioned in a plurality of the openings in the deck.22. The apparatus of claim 13, wherein the cassette comprises a rigidbase defining a recessed region, and a flexible membrane attached to thebase in a manner such that the flexible membrane, when pressed againstthe base, cooperates with a portion of the base defining the recessedregion to form a pump chamber.
 23. The apparatus of claim 20, whereinthe pump chamber has an inlet port and an outlet port.